This invention relates to antistatic agents for synthetic polymer materials and methods of applying such an antistatic agent to a synthetic polymer material. Synthetic polymer materials are usually strongly hydrophobic and hence tend to become electrostatically charged. These characteristics are a problem in the production process of such materials as well as when the products made therefrom are actually used. This invention relates to antistatic agents with which such problem can be overcome and also to a method of applying such an agent to a synthetic polymer material.
In the past, electrically conductive agents such as carbon or electrically conductive metallic powder or surfactants used to be used as an antistatic agent against synthetic polymer materials. They are usually added to such a synthetic polymer material or applied on its surface. When such an electrically conductive agent is used, however, a significantly large quantity is usually required for obtaining any appreciable effect and the method of application was not very simple. Moreover, since transparent products of this kind were hard to obtain and these agents are rather expensive, they could be used only under limited circumstances. On the other hand, there are many kinds of surfactants and it is usually possible to select an appropriate surfactant for most situations, and many kinds have been proposed for application to synthetic polymer materials. If an anionic surfactant is used, however, its compatibility is usually poor and it may not disperse uniformly. Since it tends to decompose or deteriorate when heated and to adversely affect hue or transparency, it is considered difficult to use. Cationic surfactants having quaternary nitrogen in the molecule or ampholitic surfactants have good antistatic capabilities but their resistance against heat is poor, and hence they can be used only for a limited range of purposes. Non-ionic surfactants are superior to ionic surfactants regarding compatibility with synthetic polymer materials but not only is their antistatic capability weak but it tends to become weaker with time at normal or higher temperatures. For improving the characteristics of these surfactants, Japanese Patent Publications Tokkai 62-230835, 63-117061, 1-14267, 1-62336 and 1-92474 and U.S. Pat. No. 4,943,380 have proposed the use of phosphonium sulfonates. The kinds of phosphonium sulfonates proposed in these references, however, tend to adversely affect the natural hue or transparency of the synthetic polymer materials, and since only a limited amount of them can be used, sufficient antistatic quality cannot be obtained under a low humidity condition.